Finally got the machine to stay on and was replicating the orginal posters problem exactly.
To get to that point all I did was take out the CPU and then replace the CPU ... and put it back exactly how it was before. Even though it shut off after 20 seconds I still viewed it as progress. Though was pretty bummed when it happened because at first I thought it was just going to stay on.
So, after doing this a few times I think it is the PSU. The machine seemed to shut off whenever the HD started spinning up. Well, I wanted to test a few times to see if that was indeed what was going on ... I had planned on unplugging the HD to see if it would stay on but before I got the chance one of the times I started it up I got a bright flash of light from the PSU and now I'm not getting any power at all. (Guessing something blew ... I hope it didn't fry anything else). I didn't get smoke or anything so ... at least that's a good sign.
Unfortenately I hadn't hooked a monitor up to it yet so I don't know how far into the booting process it got. I guess I'm getting a new PSU now ><
I'll keep you guys posted.
Edited by cliff283, 08 November 2006 - 10:39 AM.